Submicron binderless polycrystalline diamond sintering under ultra-high pressure

Abstract Pure diamond compacts with submicron grain size were prepared by sintering diamond powder at 14.0 GPa and 1600–2000 °C using a multi-anvil apparatus. The synthesis conditions were much milder than those required when using graphite as the precursor. The sintered polycrystalline diamond (PCD) displayed excellent mechanical properties comparable to those of nano-polycrystalline diamond. The highest Vickers hardness measured for PCD was 125.0 GPa. During sintering, the small diamond grains between larger grains transformed into graphite first at moderate sintering temperature, and then the graphite transformed into diamond at 14.0 GPa and higher temperature. The large amounts of nano-twins and stacking faults inside the diamond grains contributed to the high Vickers hardness of PCD.